The invention relates to a method for analyzing a sample on a test element in an analysis system, in particular for measuring, the concentration of glucose in a body fluid on a test strip.
In order to analyze samples, for example body fluids such as blood or urine, it is common to use analysis systems in which samples to be analyzed are situated on a test element and react in a test field if appropriate with one or more reagents on the test element before they are analyzed. The optical, in particular photometric, and electrochemical evaluation of test elements are the most commonly used methods for rapidly determining the concentration of analytes in samples. Analysis systems with test elements for sample analysis are generally used in the field of analysis, environmental analysis and primarily in the field of medical diagnosis. Test elements which are evaluated photometrically or electrochemically are of great value, particularly in the field of blood glucose diagnosis from capillary blood.
There are various forms of test elements. For example small substantially square sheets, also referred to as slides, in the middle of which there is a multilayer test field are known. Diagnostic test elements which are in the form of strips are referred to as test strips. Test elements are comprehensively described in the prior art, for example in the documents DE-A 197 53 847, EP-A 0 821 233, EP-A 0 821 234 or WO 97/02487. The present invention relates to test elements of any desired form, including strip-type, test elements.
Test elements in which a sample is applied to a sample application site and is transported by means of capillary force into an analysis region (test field) separate from the sample application site are known in the prior art. Such a test element is the subject matter of DE 197 53 847 A1, for example.
For the analytical investigation of a sample on a test element, test element analysis systems containing a test element receptacle or mount for positioning the test element in a measurement or analysis position and a measurement and evaluation device, also referred to as an analysis unit, for carrying out a measurement and determining an analysis result based on this are known in the prior art.
In order to mount the test element in the analysis position, known positioning devices have a displaceably mounted pin with an end that tapers conically towards the bottom. When suitably positioned, the tip of the pin is situated in a recess provided in the test element, with the result that the test element is fixed and positioned in the direction of its longitudinal axis. The pin can also serve to electrically signal the presence of a test element or the positioning thereof. For this purpose, the pin is embodied in electrically conductive fashion and a contact is provided e.g. on the opposite side of the apparatus to said pin. When there is no test element, the pin is pressed against the contact by means of a spring and an electrical contact is made between these two elements. If a test element is then inserted, it initially pushes itself between the pin and the contact, with the result that the electrical contact is cancelled. However, as the test element is pushed further, the pin engages through the groove in the test element and the electrical contact is closed again. The contact can e.g. also be actuated by a lateral cantilever of the pin.
In many known analysis systems, the positioning of a test element relative to an analysis unit is critical, particularly in the case of an optical evaluation of test elements. A relative positioning of the analysis region of a test element with respect to the evaluation optical system is of crucial importance for the precision and correctness of the measurement carried out for the analysis of a sample in the analysis region.
Many solutions are provided in the prior art for ensuring a correct positioning. In the above example of a positioning device, correct positioning of the test element in the longitudinal direct (X direction) is ensured as a result of the pin engaging into the recess in the test element. For positioning in the transverse direction (Y direction), the positioning device may comprise guide elements. In this and also in many other positioning devices for test elements in analysis systems, however, an incorrect positioning in a perpendicular direction with respect to the analysis region (Z direction) cannot be precluded. By way of example, a user can raise the test element at the side remote from the pin in such a way that the positioning of the analysis region relative to the analysis unit of the analysis system changes in such a way that the analysis result is corrupted. Even in the case of a mounting at both ends of a strip-type test element, for example by means of a pin engaging into a recess at one end and a holding-down device, bearing on the test element surface, at the other end of the test element, an incorrect position of the analysis region in the Z direction can occur it the test element has flexed between the two holding elements. Therefore, an analysis system for analyzing a sample on a test element must be able to identify such an incorrect positioning in the Z direction in order to avoid the indication of erroneous analysis results by the analysis system.
The object of the present invention is to provide a method for analyzing a sample on a test element in an analysis system, and an analysis system for analyzing a sample on an analytical test element which avoid the disadvantages of the prior art. In particular, in the case of the method according to the invention and the analysis system according to the invention, the object is to identify an incorrect positioning of the analysis region of a test element in the Z direction. Furthermore, the method according to the invention and the analysis system according to the invention are intended to react more sensitively to an incorrect positioning in the Z direction, particularly in the case of flexure of the test element in the Z direction in a test element receptacle of an analysis system.